This research intends to develop an oxygen sensor co-located with a biopsy needle to assist in the biopsy of tumor cells for molecular profiling of low-prevalence mutations or biomarker quantification and to permit real-time mapping of complex areas of necropsy and metathesis. Tumors can have large regions of necrotic tissue with small peripheral areas of live tumor cells or large viable tumors with small areas of necrotic tissue on the periphery. The biopsy device will provide the clinician with the resolution needed to survey and map the suspect tissue. In particular, the biopsy device will: 1) Assure sampling of viable (living) parts of a tumor, 2) Provide clinicians with oxygen levels throughout the tumor to aid in choosing the most effective treatment therapies, 3) Aid in predicting clinical outcomes during selected therapies. Partial pressure of oxygen (pO2)-guided, vacuum-assisted needles will permit the collection of multiple small-volume biopsies of tissue with different levels of hypoxia for more reliable diagnosis. A mouse model with MDA231 human breast carcinoma will be used to evaluate and demonstrate the device using CT scan imaging to place the needle/sensor tip. The University of Massachusetts Medical School will assist with the animal studies and histology.